Method for taut sheath splicing of all-dielectric self-supporting fiber optic cable

ABSTRACT

An apparatus for splicing a fiber optic cable comprises a clamp for clamping a first portion of a first fiber optic cable, a bail for connecting the clamp to a support structure, a splice closure for splicing a second portion of the first fiber optic cable to a second fiber optic cable, and means for connecting the splice closure to the bail. A method of splicing a fiber optic cable, using the apparatus is also included.

FIELD OF THE INVENTION

This invention relates to an apparatus for splicing fiber optic cable,and more specifically, to apparatus for splicing all-dielectric,self-supporting (ADSS) fiber optic cable.

BACKGROUND OF THE INVENTION

Fiber optic cables are widely used in communications systems.Communications services are typically provided to specific customers bysplicing drop cables to feeder cables.

For years, users of fiber optic cables lashed to messenger wires haveused the technique of “taut sheath splicing” to splice cables used todrop service to specific customers. The taut sheath splicing techniqueis attractive because it enables a user to splice in the drop cablewithout predetermining splice points or slack coils. The technique iscurrently performed only with messenger supported fiber optic cables,that is, cables having a messenger, typically a steel cable, as thesupporting element. The optical fibers can be either lashed to amessenger, or embedded in a “figure 8” type cable with the messenger andfiber optic cable extruded together into a “figure 8” form.

All-dielectric, self-supporting (ADSS) fiber optic cable contains nometal, and uses aramid yarns or other non-metallic strength members tominimize the amount of strain experienced by the fibers during theirlifetime. Devices that are used to connect the cables to supportingstructures must grip the cables in a manner such that the tensile loadfrom the cable is properly transferred from the cable strength membersthrough the cable sheath to the supporting structure, without damagingthe optical fibers.

ADSS cable has inherent benefits over lashed systems. Since the ADSSinstallation only requires the installation of a single cable, theinstallation method is faster, and therefore less expensive than thetwo-part installation of a lashed system. ADSS cable can more easily bedeployed in the “supply” zone of the pole, making it very attractive foruse by groups, such as municipalities, that have access to the supplyarea of the pole. The metal-free, dielectric design eliminates bondingand grounding of the cable. In addition, there is minimal maintenancerequired for the ADSS system, relative to a lashed system.

One reason that taut sheath splicing has not been performed on ADSScable is an industry perception that traditional ADSS needed a deadendbuilt into each end of the splice closure, turning the closure into astructural member.

Another reason is the industry perception that an ADSS cable must belashed within the span in the vicinity of the splice, therebydramatically increasing the cost of the installation and decreasing theflexibility of the installation.

There is, therefore, a need for an improved apparatus for permittingsplicing all-dielectric, self-supporting fiber optic cable.

SUMMARY OF THE INVENTION

An apparatus for splicing a fiber optic cable constructed in accordancewith this invention comprises a clamp for clamping a first portion of afirst fiber optic cable, a bail for connecting the clamp to a supportstructure, a splice closure for splicing a second portion of the firstfiber optic cable to one or more additional fiber optic cables, andmeans for connecting the splice closure to the bail.

The bail can comprise a metallic cable. The clamp can comprise a framehaving first and second side plates, wherein each of the side platesdefines a tapered groove, and first and second wedges are positioned inthe side plate grooves. The splice closure can be positioned away fromthe clamp to maintain a minimum bend radius in the first fiber opticcable, both during the splicing operation and once the splicingoperation is complete.

This invention is particularly applicable to splicing all-dielectric,self-supporting (ADSS) fiber optic cable.

In another aspect, the invention encompasses a method of splicing afiber optic cable, the method comprising the steps of: applying a clampto a first portion of a first fiber optic cable, using a bail to connectthe clamp to a support structure, connecting a splice closure to thebail, connecting an aerial splicing work platform to the bail, andsplicing a second portion of the first fiber optic cable to a secondfiber optic cable in the splice closure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation of an apparatus constructed inaccordance with this invention.

FIG. 2 is a pictorial representation of a clamp portion of a deadendassembly used to support a fiber optic cable.

FIG. 3 is a pictorial representation of the splice closure of theapparatus of FIG. 1.

FIG. 4 is a pictorial representation of a splice enclosure incombination with a fusion splicer that can be used in an apparatusconstructed in accordance with this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This invention provides an apparatus and method for splicingall-dielectric, self-supporting fiber optic cable. Referring to thedrawings, FIG. 1 is a pictorial representation of an apparatus 10constructed in accordance with this invention. The apparatus includes awedge type clamp 12 for gripping a first fiber optic cable 14, which maybe a feeder cable. A bail 16 is provided for connecting the clamp to asupport structure 18 using a guy attachment 20. The clamp 12 and bail 16form a deadend assembly 22. A splice closure 24 is connected to the bail16 by a connection means 26 in the form of clamps 28 and 30. The firstfiber optic cable 14 extends through the clamp 12 and into a first endof the closure 24. A second fiber optic cable 32 also extends into thefirst end of the enclosure 24. The taut-sheath splice provides access tospecific fibers inside a fiber optic cable without severing the entirecable. For example, if cable 14 includes numerous fibers, one or more ofthose fibers can be extracted from cable 14 and spliced to cable 32.Meanwhile, the remaining unsevered fibers in cable 14 continue throughthe right hand side of the closure in the portion of the cabledesignated as 34 in FIG. 1. The closure is positioned a sufficientdistance from the clamp so that a minimum bend radius can be maintainedin the portions of the fiber optic cables 14 and 32 lying between theclamp and the closure. The minimum bend radius is specified on the cabledocumentation, and will vary by cable type. The installer would be awareof the bend radius constraints of a particular cable and would positionthe closure accordingly.

The deadend assembly 22 includes the wedge clamp 12 and the bail 16. Thewedge deadend and secured bail can be attached to support structuressuch as poles or towers. FIG. 2 is a pictorial representation of thedeadend assembly 22. The wedge clamp includes a frame 40 with anattached cable bail for mounting to the support structure. The frameincludes two side plates 42 and 44. Each plate has two slots that aretapered and angled toward one another. Two wedges slide into the slotsin the frame. The wedges are similarly tapered, enabling them to beinterlocked with the side plates. Each wedge also has a groove that issized and textured to grip the cable 14. The wedges can be designed toapply pressure to the cable evenly along the entire contact surface ofthe wedge, or with varying force along such surface. The actual size ofwedge deadend depends on the specific application for which it will beused.

As cable load is applied to the wedge deadend, wedges in the clamp slideforward in a frame and tighten around the cable. These wedges grip thecable in proportion to the load on the cable. That is, the greater thecable load, the higher the load applied to the cable to secure it. Thewedges do not slide back when the load is released, thus, oscillatingloads will not loosen the wedges because they are literally wedged intothe frame. The shallow taper of the wedges allows them to move forwardin the frame significantly as the cable is loaded. By making this angleshallow, the compressive force that the wedges place on the cable for agiven cable load, and hence the tensile force placed on the frame, isincreased. The normal force of the wedges on the frame slots creates afriction force that locks the wedges in place. At the same time, theshallow angle decreases the tendency of the wedges to slide back out ofthe frame. Note that lubrication can be applied to the sliding surfacesto facilitate the wedges moving forward in the frame when the cable isloaded. The wedge deadend is designed so as to hold the cable withenough force to prevent cable slippage, but not enough force so as todamage the cable jacket or to diminish optical performance of the cable.Further, the design of the deadend permits the frame to easily be openedand closed without the use of tools. A wedge type deadend is disclosedin U.S. Pat. No. 5,647,046, which is hereby incorporated by reference.In this invention, the deadend includes an extended bail that supports asplice closure. The clamping mechanism portion of the deadend can beconstructed in accordance with known designs.

Cable 32 is a drop cable that is connected to the feeder cable 14 in thesplice closure 24. Fiber optic cable 34 can be a section of cable 14 ora separate fiber optic cable that is spliced to cable 14 in the spliceclosure. Ordinarily, a single drop cable would have exited on the sideof the pole. However, where multiple drop cables are used, cable 32would have led to a slack-storage device which would have reversed itsdirection and brought it back to the pole.

FIG. 3 is a pictorial representation of splice closure 24 of FIG. 1. Theclosure comprises a housing 50 having two sides 52, 54 connected byhinges 56. Ports 58, 60, 62 and 64 are provided at the ends of thehousing so that fiber optic cables can pass though the ports. Splicescan then be made within the closure.

FIG. 4 is a pictorial representation of the splice closure 24 incombination with a fusion splicer 70 that can be used in an apparatusconstructed in accordance with this invention. The fusion splicer 70 issupported by a tray 72 that can be connected to the bail by a connectionmeans 74. The fusion splicer, tray, and connection means form an aerialsplicing workstation.

This invention incorporates the use of an aerial taut sheath closurewith wedge-type ADSS cable deadend hardware. Taut sheath splicing ofADSS fiber optic cable can be performed without including any plannedextra cable at installation.

The splice closure is attached at the pole location to the bail of thedeadend. The extended bail enables attachment of the weather-tightclosure, and releases the cable tension over a sufficient distance toenable the taut-sheath splice. The long bail allows flexibility for thelocation of the aerial splicing workstation, and smoothes the bends ofthe cable as they come from the deadend clamp into the splicer andsplice closure. The splice closure is designed to be compatible with“taut sheath” applications. The splice can be performed with a fusionsplicer supported by the bail of the deadend.

Since ADSS cable has not been spliced using taut sheath methods in thepast, a significant advantage of this invention is that it allowssplicing of ADSS cables without predefining the splice locations, andaccommodating them by incorporating extra cable during installation atthose locations. This advantage is particularly important for marketsthat require multiple drops to subscribers, such as for networks withina city or municipality, and for fiber to the home (FTTH) or fiber to thesubscriber applications. Since each predefined splice location alsoentails deploying extra cable and a storage method, this inventionprovides significant material and labor savings for the user. Thecapability of taut sheath splicing significantly decreases the amount ofprior planning needed when deploying a network, thereby savingsignificant amounts of engineering time and increasing the flexibilityof the network, while also keeping the inherent benefits of ADSS cableas described above.

In addition to the apparatus described above, the invention encompassesa method of splicing a fiber optic cable. The method comprises the stepsof: applying a clamp to a first portion of a first fiber optic cable,using a bail to connect the clamp to a support structure, connecting asplice closure to the bail, connecting an aerial splicing platform tothe bail, and splicing a second portion of the first fiber optic cableto a second fiber optic cable in the splice closure.

This invention is particularly applicable to splicing all-dielectric,self-supporting (ADSS) fiber optic cable. The ADSS cable can include aplurality of optical fibers which can be accessed without severing theADSS cable or requiring additional slack in the ADSS cable to perform asplice.

While particular embodiments of the invention have been described indetail for the purposes of illustration, it will be evident to thoseskilled in the art that numerous variations may be made to the disclosedembodiments without departing from scope of the invention as defined inthe appended claims.

1. A taut sheath splicing apparatus comprising: a self supporting fiberoptic cable clamp; a bail connected to the self supporting fiber opticcable clamp; and a splice closure connected to the bail.
 2. The tautsheath splicing apparatus of claim 1, wherein the bail comprises ametallic cable.
 3. The taut sheath splicing apparatus of claim 1,wherein the self supporting fiber optic cable clamp comprises a wedgeclamp.
 4. The taut sheath splicing apparatus of claim 3, wherein thewedge clamp comprises: a frame having first and second side plates,wherein each of the side plates defines a tapered groove; and first andsecond wedges positioned in the side plate grooves.
 5. The taut sheathsplicing apparatus of claim 1, wherein the splice closure is positionedaway from the clamp to maintain a minimum bend radius of a fiber opticcable clamped by the clamp.
 6. The taut sheath splicing apparatus ofclaim 1, wherein the splice closure is a taut-sheath splice closure. 7.The taut sheath splicing apparatus of claim 1, wherein the spliceclosure is connected to the bail by at least one clamp.
 8. The tautsheath splicing apparatus of claim 1, wherein the self supporting fiberoptic cable clamp is configured to apply an even pressure to a fiberoptic cable along the contact surface of the clamp.
 9. The taut sheathsplicing apparatus of claim 1, wherein the self supporting fiber opticcable clamp is configured to apply a varying pressure to a fiber opticcable along the contact surface of the clamp.